Goods that have been cast have various shapes. To improve productivity, the number of cavities in a mold, namely, multicavity molding, has been increased. Further, various combinations of goods are used. As a result, various patterns for pouring molten metal into molds are required. Thus controlling pouring rates is important.
For example, when the ladle capacity is 500 kg, the pouring weight, the pouring time, and the pouring rate are generally set to be 10 to 50 kg, 4 to 12 seconds, and 1 to 5 kg/second, respectively. When the ladle capacity is 1,000 kg, they are generally set to be 30 to 150 kg, 6 to 15 seconds, and 5 to 10 kg/second. The pouring operations are complicated, but must be accurate. Incidentally, the term “pouring weight” means the weight of the molten metal that has been poured into a mold, and the term “pouring rate” means the flow rate of the molten metal that is being poured from a ladle into a mold.
Conventionally, an automatic pouring method has been known by which molten metal is poured by adjusting the angular velocity so as to tilt a ladle at a predetermined angle by means of feedback control. The predetermined angle is determined so as to follow a pouring pattern that is based on the pouring that is actually carried out by a skilled operator (see Japanese Patent No. 3361369, Japanese Patent Laid-open Publication No. H09-239524, and Published PCT Japanese Translation No. 2013-544188). By the method disclosed by Japanese Patent No. 3361369, the angular velocity to tilt a ladle is corrected by a correction factor that is preliminarily stored so as to maintain the constant pouring rate. By the method disclosed by Japanese Patent Laid-open Publication No. H09-239524, during the final part of the pouring the pouring weight is detected or the level of the surface of melt at a sprue is detected by means of a camera for image processing, so as to stop the pouring. By the method disclosed by Published PCT Japanese Translation No. 2013-544188, pouring patterns for various molds are easily determined by using a pouring weight, a pouring time, and a predetermined pouring pattern. These methods that are disclosed by the prior-art publications are only effective for the particular problems. However, they are not sufficient to automatically control the pouring rate.
By a typical and conventional pouring, molten metal is poured into a sprue for about two seconds by increasing the pouring rate so as not to spill it, so that the gating system is filled with the molten metal. After the molten metal starts to fill the cavity, the pouring rate is adjusted to follow the flow of the molten metal to the cavity while the sprue is watched so that no molten metal spills out. A skilled operator stops the pouring by judging the completion of the pouring based on his or her experience.
However, understanding the progress of the pouring is difficult. If the flow is too little, the temperature of the molten metal decreases or the shapes of molds change, to cause a misrun. On the other hand, if the flow is too great, the molten metal scatters or overflows. Further, estimating the amount of the molten metal that flows into a cavity is difficult. The pouring rate is generally reduced to prevent overflow, so that the pouring time become longer. This operation directly and negatively affects the productivity.
If the operation of the pouring from the beginning to the end of the pouring is controlled only by a deviation between the predetermined pouring pattern and the actual measurements, the delay in the change of the pouring rate causes the molten metal to leak, to overflow, or to have a short run.
If the pouring rate is controlled only by means of the flow of the molten metal into the cavity by using a model based on the relationship between an elapsed time and a flow rate that is based on the flow of the molten metal into the cavity, the operation tends to be carried out so as to ensure safety, so that the pouring time may be lengthened or so that the temperature of the molten metal decreases. Further, no deterioration of the nozzle of the ladle can be dealt with.
To enhance productivity there are strong requirements to shorten the pouring time and to increase the pouring rate. Thus a leak of the molten metal in which the molten metal leaks from the sprue or the molten metal overflows is highly possible. Further, the decrease in the temperature of the molten metal, the adhesion of slag to the nozzle of the ladle, or changes of the shapes of the molds, cause the direction of the flow of the molten metal to change. Thus controlling the flow rate becomes difficult.
The present invention aims to provide a pouring machine and method by which the level of the surface of melt can be constantly maintained from the beginning to the end of the pouring and by which the pouring can be carried out for a proper pouring time without a leak of the molten metal, an overflow, a shrinkage, or a short run, to maintain a necessary and sufficient pouring rate.